Michigan Technological University Digital Commons @ Michigan Tech Dissertations, Master's Theses and Master's Dissertations, Master's Theses and Master's Reports - Open Reports 2014 RELATIONSHIP BETWEEN STATIC STRESS CHANGE AND VOLCANISM. HOW AND IF TECTONIC EARTHQUAKE COULD INFLUENCE VOLCANIC ACTIVITY. EXAMPLE OF EL REVENTADOR VOLCANO, ECUADOR Daniele Alami Michigan Technological University Follow this and additional works at: https://digitalcommons.mtu.edu/etds Part of the Geology Commons, and the Volcanology Commons Copyright 2014 Daniele Alami Recommended Citation Alami, Daniele, "RELATIONSHIP BETWEEN STATIC STRESS CHANGE AND VOLCANISM. HOW AND IF TECTONIC EARTHQUAKE COULD INFLUENCE VOLCANIC ACTIVITY. EXAMPLE OF EL REVENTADOR VOLCANO, ECUADOR", Master's report, Michigan Technological University, 2014. https://doi.org/10.37099/mtu.dc.etds/770 Follow this and additional works at: https://digitalcommons.mtu.edu/etds Part of the Geology Commons, and the Volcanology Commons RELATIONSHIP BETWEEN STATIC STRESS CHANGE AND VOLCANISM. HOW AND IF TECTONIC EARTHQUAKE COULD INFLUENCE VOLCANIC ACTIVITY. EXAMPLE OF EL REVENTADOR VOLCANO, ECUADOR. By Daniele Alami A REPORT Submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE In Geology MICHIGAN TECHNOLOGICAL UNIVERSITY 2013 © 2013 Daniele Alami This report has been approved in partial fulfillment of the requirements for the Degree of MASTER OF SCIENCE in Geology Department of Geological & Mining Engineering & Sciences Report Co-Advisor: Gregory P.Waite Report Co-Advisor: Alessandro Tibaldi Committee Member: Simon Carn Department Chair: John Gierke 1 2 L'infinito non esiste, è solo un numero grande, e l'unico vero cuore è al centro della Terra. Vai davanti a un vulcano e poi dimmi, come ti senti? (Filippo Timi) 3 Università degli studi di Milano-Bicocca Facoltà di Scienze Matematiche, Fisiche e Naturali Dipartimento di Scienze e Tecnologie Geologiche Relationship between static stress changes and volcanism. How and if tectonic earthquakes could influence volcanic activity. Example of El Reventador volcano, Ecuador. 4 Introduction Geological setting of the area Pre-Pleistocene structural setting of Ecuador Latest Pleistocene – Holocene of Ecuador Seismic background Seismicity due by subduction conditions on the Ecuadorian margin Seismicity of the Napo province and around El Reventador Volcano background Structural background on the edifice Petrological characteristic of the product Methods of modeling Numerical mode: developed by 3.2 Coulomb software Conceptual model and elaboration Results Results by field evidence Results by modeling Discussion and conclusion Attachments (at the end of the book) Table A, B, C Acknowledgments Bibliography 5 Introduction Particular conditions of the subduction zone along the Ecuadorian margin has a big influence on the behavior of the structures, which surround all the volcanoes, present in the Ecuadorian territory. A lot of attention I dedicated on El Reventador because it is an active volcano, which alternate periods of rest with violent explosion when the activity start again, and periods of effusive emission gas, ashes and lava flows. This activity could probably have some link with the movement inside the crust, in the region of this volcano and the biggest eruptive event as well. Here we consider the last two century of seismic event from the 1800 to the present basing our study on different seismic catalogues taking in account just the seismic events which has a magnitude M>3 included in a distance within less than 100 kms in particular the 5th March 1987 earthquake. Some eruptive events of Reventador volcano have often accompanied by some earthquakes in Andean chain more or less close to this edifice. Especially during the last decades few seismic episode around the Napo province, with various depth and magnitude, were recorded and evaluate to see if this episodes could influence the recent eruptive history of this volcano. El Reventador volcano is fortunately located not too close to the principal Ecuadorian City Quito, located more than 70 kms, but during some particular violent explosion, the ashes clouds moreover, the pyroclastic flows could interact with it. Further than, near the volcano there are a lot of small villages inhabited by poor people without good acknowledgments about how to prevent the risk and a hydroelectrical line runs all along the province, with an high probability to be destroy if the volcanic events should be more intense or anomalous. To calculate if it is possible obtained a significant relation between the two events, we had to consider in what way changes the static stress could modify the condition all around 6 the magmatic chamber and consequently if it is able to induce magmatic activity. With the software Coulomb 3.1, we could model the activity of some specific oriented faults and see how much and in what way the static stress could change in the crust and around the magmatic complex. Obviously the two phenomena are far away to be in a linear relationship that would be BIG EARTHQUAKES=BIG ERUPTION but try to understand if a succession of some kind of seismic events could lead to dangerous or anomalous volcanic episode with a big importance for the forecasting and the risk prevention. This because a magmatic system, being composes by several physical phases, is particularly susceptible to sudden surrounding stress change. Further this calculation, the results obtained for the static stress change could be processed consequently in another software, to be part of a probabilistic model to identify if the earthquakes could produce changes and guiding the volcano behavior. That is mean, we are looking on our models not just to define if an earthquake is accountable for a certain volcanic event, but also to provide, with some degree of liberty, which cause could be more significant than others could. It is possible to use this software to analyze the various probability of an eruption in a long or short time windows; the procedure to make this survey are described later in one of the last chapter where I am going to talk about the method of modeling. Geological Settings Pre-Pleistocene structural setting In the Andean chain in Ecuador, the parallel ranges of the Cordillera Occidental and the Cordillera Real are separated by the narrow depression of the InterAndean Valley and connected 5 to the Amazonian Platform by the Subandean Zone foothills (fig.1 on the left). Studied area Fig.1: Oblique subduction between South America Plate, Nazca Plate and Caribbean Plate (left). Highlited studied area; red triangle represent El Reventador volcano. Circle is the survey area (right). The Ecuador margin (3.0°N–3.5°S) represents a region of intense crustal deformation, related to the oblique subduction of the oceanic Nazca plate beneath the South-American continental plate, along a N90°E direction and at a rate of ∼58mm/yr (after Trenkamp et al., 2002) (fig. 1 on the Alendft).ea Tnh eblo mcakrg einxpul undsionerg oaet s∼ s6hor mmten/ying (a fpteerrp Terndienkcaumplar teot tahl.,e t2002)rench taox theis, in Nvoroltvhienags t,the pa norralltehl to the margin. This oblique subduction zone has a big influence on the structures within the crust on the landside of Ecuador forming, adding to the typical faults of this kind of subduction zone. The Ecuadorian margin consists of the oceanic North-Andean block, which was accreted to the Brazilian continental craton during the Cretaceous (Jaillard et al., 1997). These oceanic terranes 6 forming the Ecuadorian margin substratum seem to extend southward into northern Perù (Shepherd and Moberly, 1981). They consist of tholeitic/andesitic basalts and pillow lavas associated with siliceous sediments, defined as the Piñon Formation. In Ecuador, the Piñon Formation is overlain by an intra-oceanic volcanic arcs series, such as the Cayo formation. To the north (south Colombia, Gorgona Island), outcrops of Cretaceous oceanic terranes (mafic to ultramafic rocks) are associated with the Diabasico Formation (Goosens et al., 1977; Marriner and Millward, 1984; Mamberti et al., 2004). Several studies on deformation of Andean coastal basins have shown that the margin has undergone a generally compressive regime since accretion of the oceanic terranes to the Ecuadorian paleomargin (∼90 My ago). This compressive regime appears largely disturbed in the Gulf of Guayaquil (GG) area, where the tectonic structures testify a N–S trending opening of the GG basin (fig.2). Wide angle seismic models obtained by travel time inversion at the Ecuadorian convergent margin reveal variations in the crustal structure of the subducting Nazca plate and the overriding South American plate that strongly control the deformation of the margin and the seismic cycle : The overriding plate is characterized by a well developed Cretaceous oceanic substratum, described on land as the Diabasico and Piñon formations, underlain by high seismic velocities (5.5–6.2 km/ s). The structure of the margin suggests it was affected by transient phases of erosion and accretion. The inner part of the margin shows a large low velocity zone. Its upper limit correlates with a major splay fault that originates on the inter-plate contact zone and could have favored the propagation of the 1958 great earthquake rupture (Collot et al., 2004). The Central Zone reveals an over-thickened oceanic crust (15 to 19 km) beneath the CR. The Cretaceous oceanic basement is well developed and is likely to have been uplifted beneath the margin. The buoyancy of the Nazca plate and the high density of the margin basement both contribute to an increased 7 Fig.2: General map of the eastern part of the Nazca plate and of the southern Colombia and Ecuador margin. Stars: epicenters of the six great subduction earthquakes that occurred along the margin since 1901, including four in the Northern part (3.5°N–0.5°S). (Beck and Ruff, 1984; Mendoza and Dewey, 1984). inter-plate coupling. The fore-arc shows neither evidence of subsidence or for frontal accretion.